Circ_DLG1 facilitates cell proliferation and metastasis of esophageal squamous cell carcinoma via upregulating MAP3K9.

Background: Circ_DLG1 is found to be aberrantly expressed in esophageal squamous cell carcinoma (ESCC) tissues, but its role in the progression of ESCC remains to be elucidated.

Methods: The expression of circ_DLG1, miR-338-3p and mitogen-activated protein kinase kinase kinase 9 (MAP3K9) was measured by qRT-PCR. Cell cycle, viability, migration and invasion were investigated using flow cytometry, MTT assay and transwell assay, respectively. The protein levels of MAP3K9, p38, phosphor p38 (p-p38), ERK1/2 (ERKs), phosphor ERKs (p-ERKs) were detected by western blot. Dual-luciferase reporter assay and RIP assay were performed to verify the putative relationship between miR-338-3p and circ_DLG1 or MAP3K9. Animal experiments were performed to ascertain the role of circ_DLG1 in vivo.

Results: Circ_DLG1 expression was elevated in ESCC tissues, plasma and cells. Circ_DLG1 knockdown inhibited cell proliferation, migration and invasion. MAP3K9 was highly expressed in ESCC, and its overexpression rescued the effects of circ_DLG1 knockdown on cell proliferation and metastasis. Besides, circ_DLG1 positively regulated MAP3K9 expression by competitively targeting miR-338-3p. Also, miR-338-3p inhibition or MAP3K9 overexpression recovered the inhibiting effect of circ_DLG1 knockdown on the phosphorylated levels of p38 and ERKs. In addition, circ_DLG1 knockdown blocked the tumor growth in vivo by regulating the miR-338-3p/MAP3K9 axis.

Conclusion: Circ_DLG1 promoted malignant progression of ESCC by mediating the miR-338-3p/MAP3K9/p38/ERK pathway, indicating that targeted inhibition of the circ_DLG1/miR-338-3p/MAP3K9/p38/ERK axis might be an effective strategy for the treatment of ESCC.